It is common practice to employ FETs having insulated gates in switching converters and inverters. A problem is that at low power significant energy is lost in the gate capacitance of the FETs. This loss is due to the fact that the insulated gate must be continually charged and discharged as the FET is turned on and off.
The energy stored in the gate capacitance is 1/2CV.sup.2, and V is the gate drive source voltage. With conventional gate drive circuitry, the energy transfer efficiency is limited to 50%. Furthermore, with conventional circuitry, none of the gate energy is captured upon turn-off. Accordingly, the energy consumed from the gate drive source is at least CV.sup.2 per switching cycle, and the corresponding power consumption is at least CV.sup.2 f, where f is the switching frequency.
However, if gate charging efficiency can be improved beyond the conventional 50%, and/or if a portion of the gate energy can be recovered upon turn-off, then gate drive power losses can be reduced. Besides improving overall energy conversion efficiency, such an improvement will also enable increased frequency operation in those cases where gate losses are a significant portion of the switching losses.